This invention relates generally to fabricating integrated circuits and, particularly, to techniques for using photoresist to pattern features on semiconductor structures.
A photoresist may be formed over a semiconductor structure. The photoresist may be selectively exposed to radiation. Regions of the photoresist that are exposed to radiation may be more or less susceptible to attack by subsequent etching processes. Thus, by exposing a pattern on the photoresist, the photoresist may be patterned to have a particular profile. This profile may then act as a mask for subsequent processes to remove underlying material, for example, in the desired pattern.
In photoresist patterning techniques for forming relatively small features, it is desirable to control the photoresist profile to prevent undercutting of a developer sensitive substrate. A substrate is any material that is positioned under the photoresist and can include antireflective coatings and resist release layers. A resist release layer is a layer that is utilized to facilitate the release of the resist after the patterning is completed. In particular, it may be desirable to control resist profiles to enhance pattern fidelity at the bottom of printed features, such as trenches and holes.
One technique for using photoresist is called the Shipley lift-off layer (LOL). The LOL facilitates removal of the photoresist after patterning and etching and is one type of resist release layer. The LOL is easily attacked by the photoresist developer. The photoresist developer is utilized to develop the material after exposure. Since the LOL is easily attacked by that developer, lifting or peeling of the photoresist may occur prior to etching.
However, intentionally underdeveloping the photoresist leaves a thin layer of photoresist over the LOL, preventing the developer from attacking the LOL. This may be followed by a descum step to break through the remaining resist and LOL. This process may be followed by standard etching of the underlying substrate. While this procedure has promise, it is difficult to control and has relatively little process margin.
Thus, there is a need for better ways to control photoresist profiles.